This project will build on existing surveillance systems for breast cancer detection and diagnostic procedures among 92,000 women aged 35 and above. These women are enrollees of a health maintenance organization, Group Health Cooperative of Puget Sound (GHC), which established a formal breast cancer screening program in 1985. Current independent automated clinical systems include mammography, pathology, cost, breast cancer risk factor, and clinical breast examination data on most women age 35 and above. Cancer outcomes are captured by the SEER registry. The core activity of the project will enhance and link existing data systems to improve their usefulness for research. Specific activities include: 1) implementing the American College of Radiology lexicon for standardized interpretation and reporting all mammography examinations, 2) enhancing the pathology system to capture histologic findings, and 3) creating a breast tissue registry that links biopsy dates, findings and breast cancer risk information. Prior experience with surveillance research, and ability to build on an existing data system, will assure rapid provision of high quality, detailed data, make the investigative team a strong contributor to collaborative analyses. The core activities will support two Surveillance Initiatives and four Research Projects. Surveillance Initiative 1 will monitor population rates of mammography and clinical breast examination among symptomatic and asymptomatic women, record rates of diagnostic service usage, and evaluate the sensitivity, specificity, and positive predictive value of screening and symptomatic mammography. Surveillance Initiative 2 will document the effectiveness of breast cancer screening in our population and that of the surrounding area, using our existing linkage to the western Washington SEER system. the Research Projects will investigate 1) cellular differences in normal and malignant breast tissue using biomarkers; 2) the costs of alternative diagnostic strategies; 3) methods to improve the quality of mammographic interpretation. The results of the project will contribute to improvements in breast cancer detection and diagnosis, implementation of breast cancer screening, and our understanding of breast cancer biology.